When a patient receives an intravenous solution, the flow rate of the solution into his blood stream must remain at or below a "safe" level. When the flow rate exceeds that level, the patient may suffer several deleterious consequences.
R. Scott Turner et al., in their U.S. Pat. No. 4,121,584 and entitled "Method and Apparatus For Controlling the Dispensing of Fluid", interpose a metering unit into the actual flow stream of the intravenous solution before it reaches the patient. They also provide a control unit which cooperates with the metering unit to provide a specified number of increments of fluid to the patient during particular time spans.
In operation, the control unit opens an inlet valve in the metering unit to allow fluid to enter a metering chamber having a defined maximum volume. After sufficient fluid has entered to fill that chamber, no further fluid can enter although the inlet valve may stay open. After the metering chamber has filled, however, the control unit closes the inlet and opens and outlet valve. The fluid within the metering chamber may then pass through the outlet to the patient.
After the metering chamber empties, the control unit closes the outlet valve and again opens the inlet to start another cycle of operation. The frequency of the cycles determines the maximum flow rate of solution received by the patient.
In the Turner, et al. patent, valving takes place by means of valve actuator pins which press a membrane against a land to effect closing of the inlet or outlet.
In accordance with this invention, an improved valving means is provided which requires less criticality of manufacture for providing effective inlet and outlet valves, for precise control of fluid flow in preferably a parenteral solution set.